Systems which permit the weighing of vehicles in motion are called
Systems which permit the weighing of vehicles in motion are called dynamic Weigh-in-Motion scales. the Weigh-in-Motion site. Tests carried out in the climatic chamber allowed the influence of temperature on the sensor intrinsic error to be determined. The results presented clearly show that all kinds of sensors are temperature sensitive. This is a new finding, as up to now the quartz and bending plate sensors were considered insensitive to this factor. is computed from Equation (1). = 1, 2, , and dissipation factor of a piezoelectric polymer sensor; (b) dissipation factor tg(), for 1: sensor with connecting cable, 2: sensor without connecting cable. The weighing intrinsic error arises from the difference between the actual sensor temperature value and the reference temperature value at which Rabbit Polyclonal to Osteopontin the WIM system was calibrated (in this test the reference temperature was +20 C). The relative value of the error is computed from Equation (1). The plot of error (1) versus the sensor temperature is shown in Figure 9. As follows from this characteristic, a rise in temperature of 20 C over the reference temperature results in a weighing error of about 4%. At extremely low temperatures this error may be contained within the range 10%C20%. Figure 9 The weighing error in a WIM system equipped with piezoelectric polymer sensors, arising exclusively from a change in the sensor parameters due to a change in temperature (intrinsic error). 4. Conclusions and Future Work Achieving a high and known accuracy of WIM systems will enable their use for direct enforcement purposes. Due to the influence of numerous Alizarin factors limiting this accuracy, this is not an easy task. The shape of the characteristic in Figure 3, and at the same time the sensitivity of the weighing results to temperature changes, depends on the pavement mechanical properties and varies from site Alizarin to site. An explanation of system behavior would require to take a stiffness model of the pavement into account. This model is complex and nonlinear in nature with three variables: the stiffness coefficient, vehicle speed and axle load. This will be the aim of further studies in cooperation with the Gdansk University of Technology. The unequal temperature distribution along and across the WIM site may also be the cause of significant weighing errors. In order to limit the influence of this factor, it is essential to install at least two temperature sensors located at the ends of each load sensor. Locations in which this unequal distribution is highly likely (such as densely urbanized areas, areas where tree shadows influence pavement temperature, or road infrastructure objects) should also be avoided as WIM sites. Finally, comparing the characteristics determined for polymer sensors shown in Figure 3 and Figure 9 allowed two causes of the weighing errors to be separated quantitatively. The influence of the sensor intrinsic error was ?12% to +2%, and the influence of the pavement parameter change (sensor external error) was ?30% to +20% over a temperature change range of ?20 C to +30 C. The intrinsic sensor error caused by the temperature change is dependent on the technology and materials used in its manufacture. In the authors opinion, the pavement temperature is a significant influencing factor; moreover, its value varies over a wide range in relatively short time intervals. This phenomenon concerns all kinds of sensors: polymer, quartz and bending plate load sensors. The results presented show clearly that in the case of the Lineas load sensors manufactured by Kistler, their temperature sensitivity, after installation in the pavement, was about 7% within the temperature range of ?10 C to +30 C. It is therefore necessary to reconsider views about the method of WIM system calibration and assessing Alizarin their accuracy using the pre-weighed vehicle method proposed in COST 323 . In the future, Alizarin accurate Multi-Sensor.